Conventionally, various proposals have been made in the field of original digital data authentication. For example, according to the invention disclosed in Japanese Patent Laid-Open No. 2000-285024, the nature of a paper's originality is provided to digital data to improve the verification performance of the digital data. More specifically, upon saving digital data in a server, a file property code indicating an original is appended to the digital data, so that the digital data can be saved and uniquely identified from at least other digital data.
Japanese Patent Laid-Open No. 2001-202436 proposes an electronic application system which assures security of application documents which are transmitted from terminals and are saved in a server for years. According to the electronic application system disclosed in Japanese Patent Laid-Open No. 2001-202436, a document storage device that saves digital data as application documents is provided, and the presence/absence of tampering is detected on the basis of information which is transmitted from a terminal and includes an application document so as to calculate a tampering detection code. After that, the transmitted information is saved in the document storage device together with the tampering detection code.
Furthermore, Japanese Patent Laid-Open No. 2000-224407 discloses an arrangement which appends a message digest value on a recording medium such as a paper sheet in a form that can hardly be tampered so as to improve the reliability of a printout upon printing digitally signed digital data.
However, when all digital data as originals are saved in a server and are managed by that server as in the inventions disclosed in Japanese Patent Laid-Open Nos. 2000-285024 and 2001-202436, a large-scale storage device must be prepared on the server side, and its maintenance and management become complicated. Also, in the case where all digital data are held on an external storage device to the server or the like over a long period, it becomes improper in terms of security.
The invention disclosed in Japanese Patent Laid-Open No. 2000-224407 proposes a strategy required to improve the reliability of a printout upon printing digitally signed digital data. In the case, not only the originality of that printout is assured, but also the registration date or the like of the printed digital data as an original is specified, thus it is more convenient for an user to use such printout.